Piezoelectric crystal apparatus



Jan. 3, 1946. R. SYKEs 2,392,429

PIEZOELECTRIC CRYSTAL APPARATUS Filed March 28, 1944 co/vouc T/VE CEMENTBVUQQQWOMM ATTORNEY Patented Jan. 8, 1946 v PIEZOELECTRIC CRYSTALAPPARATUS Roger A. Sykes, Fanwood, N. J., assignor to Bell TelephoneYork, N.

Laboratories, Incorporated, New Y., a corporation of New YorkApplication March 28, 1944, Serial No. 528,388

17 Claims.

This invention relates to piezoelectric crystal apparatus andparticularly to mounting arrange ments for piezoelectric crystalelements, such as wire supported thickness mode quartz crystal elements,useful as circuit elements in oscillation generator systems and in othersystems utilizing electromechanical vibratory elements.

One of the objects of this invention is to provide improved mountingarrangements for piezoelectric crystal elements such as wire supportedquartz crystal plates having integral or adherent electrode coatings andoperating in thickness mode vibrations of the shear type.

Another object of this invention is to improve the operating stabilityand frequency stability of piezoelectric crystal units.

In piezoelectric crystal elements of the high frequency type employingthickness modes of vibration and operating at relatively largeamplitudes of motion, it has been diiilcult heretofore to utilizeelectrode coatings thereon of the adherent or integral type withoutgradually wearing away the integral coatings and eventually opening thecircuit connections at the points of support. Moreover, in the case ofwire supported crystal elements it has been difilcult to keep thesupporting wires attached to the integral coatings of a thickness modecrystal element for any considerable period of time.

In accordance with this invention, a spring wire supporting system maybe provided for a thickness mode type of crystal element which does notwear away the relatively thin integral coatings of the crystal elementat the points of support and which will remain attached theretoindefinitely in operation. For this purpose the coated crystal elementmay be mechanically supported and electrically connected at any two ofits corners, such as two diagonally opposite corners thereof, by meansof a pair of separate spring wire coils, each of which may have itsadjacent turns sprung over and straddling one of the corners of thecrystal element and adhesively secured as by solder, conductive plasticcement, or electroplating for example, to that part of the integralelectrode coating that is adjacent the corner of the crystal element.The spring wire coil may be made from a relatively fine spring wirecoiled in helical, spiral or other suitable form to provide adjacentcoil turns which may be sprung over the corner edge of the crystalelement and there exert a compression force on the corner of the crystalelement in the direction of the thickness or thin dimension of thecrystal element. The compression force exerted by the spring wire coilmay selectively control the amount of mechanical damping of unwantedmodes of motion in the corner portion of the crystal element. The springwire coils may serve as an electrical connection agent and also as asupporting agent for the crystal element. The spring wire supportterminated in the spring wire coil having its.adjacent turns sprung overthe corner edge of the crystal element provides a flexible form ofcrystal mounting that does not tend to come oil in use or to wear awaythe crystal coating during long periods of operation of the unit.Moreover, the coil turns being tightly sprung over the crystal cornerare more Or less self-retaining in position and accordingly may beeasily held in place by means of a relatively light adhesive means suchas conductive plastic cement composed, for example, of finely dividedsilver or other metallic powder admixed with Bakelite or other suitablecement. Such conductive plastic cement may have little adverse effect onthe reactance-resistance ratio Q of the crystal element when subjectedto temperature variation, and moreover may be utilized in connectionwith certain crystal elements composed of crystalline material whichwill not stand the relatively high temperatures generally required whenusing a solder, such as silicon or other solder, as an adhesive agentfor securing the wire to the crystal coating. The conductive plasticcement or other adhesive agent may serve both as an electricalconnection agent and as a mechanical mounting agent for the crystalelement, and also may function as a means for reducing unwanted modes ofmotion in the corner of the crystal element, particularly when theadhesive cement is in plastic form.

The crystal electrode coatings may be partial or reduced area electrodecoatings which may extend to two opposite corners of the crystal elementand which may consist of a layer of gold, for example, applied in theform of gold bright, evaporated gold or in the form of baked metallicpaste to the bare quartz or other crystalline material. The inner orinitial coating of gold bright, when gold bright is used as the basiccoating, may then be electroplated with a coating of nickel, forexample, to the correct frequency for the coated crystal element, oralternatively an additional coating of gold, silicon film or othermaterial may be added to adjust the coated crystal element to thedesired final frequency.

For a clearer understanding of the nature of this invention and theadditional advantages, features and objects thereof, reference is madeto the following description taken in connection with the accompanyingdrawing, in which like reference characters represent like or similarparts, and in which:

Fig. 1 is an enlarged view partly in section of a crystal unit embodyingthe invention;

Fig. 2 is a greatly enlarged view showing the corner mountingarrangement of the crystal element illustrated in Fig. l; and

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2.

Referring to the drawing, Fig. 1 is an enlarged view, partly in section,of a piezoelectric crystal unit comprising a thin quartz or otherpiezoelectric crystal plate or element I provided with a pair ofmetallic or other conductive electrode coatings 2 and 3 adhering to andformed integral with selected parts of the opposite rectangular orsquare major surfaces thereof, and mounted at two of its diagonallyopposite comers by means of a pair of conductive equal length springwires 6 and 5, each of which at one of the ends Ia and 51: thereof maybe coiled in the form of a helical spring which has its adjacent turnstightly sprung over the edges of the diagonally opposite corners of thecrystal element I in individual electrical contact with the cornerextension tabs of the corresponding crystal electrode coatings 2 and 3.

The crystal element I may be a thickness mode quartz or other crystalplate having square or rectangular shaped major faces of selecteddimensions and having a thickness or thin dimension made of a valuecorresponding to the value of the desired thickness mode frequency. Theelectrodes 2 and 3 disposed on the major faces of the crystal element Iprovide an electric field for operating the crystal element I at itsdesired frequency which may be determined mainly by the thickness of thecrystal element I at the region thereof within the influence of theelectric field provided by the electrodes 2 and 8.

In a particular case, the crystal element I may be a thickness shearmode quartz crystal plate of the AT or BT cut type as disclosed, forexample, in Lack, Willard and Fair Patent 2,218,200, dated October 15,1940, and in G. W. Willard Patent 2,218,225, dated October 15, 1940.Such AT and BT cut quartz plates operate in the shear mode of motion ata frequency which is determined mainly by the value of the thickness orthin dimension thereof. The width and length major face dimensionsthereof may be made of relatively large values or at least of not toosmall values with respect to the value of the thickness dimensionthereof in order to secure good activity for the crystal plate. This isfor the reason that the activity of such thickness shear mode quartzcrystal AT or BT cut quartz plates, is a function of the size of themajor face area of the crystal plate, a factor which limits the minimumsize for the major face area of the crystal plate that may be usedeffectively. For small thickness shear mode crystal plates which have amajor face area that is already relatively close to the minimum majorface area permissible, the activity thereof may be increased roughly inproportion to the size of the effective field area provided by theelectrodes 2 and 3 since the activity of the crystal plate I is also afunction of the size of the partial field producing electrodes 2 and 3.

Also, the width and the length dimensions of the major faces of such ATand BT cut quartz plates may be relatively so proportioned with respectto the value of the frequency determining thickness dimension as toavoid interference with nearby spurious modes of motion therein such asundesired overtone flexures, shears and other more complex undesiredmodes of motion that may be present therein, as disclosed in R. A. SykesPatent 2,306,909, dated December 29, 1942. Such major face dimensioningof the crystal element relative to the thickness dimension thereofremoves the more serious effects of spurious modes of motion therein andresults in obtaining a more constant activity for the crystal elementover a wide temperature range. The most serious interfering modes arethose resultin from flexure modes in the X-Y' plane propagated along theX axis, shear modes in the X--Z plane of high order along the X axis andsheen modes in the X-Z' plane of high order along the Z' dimension. TheX and Z major face dimensions of the crystal plate should then be chosensuch that high orders of the above-mentioned interfering modes are notnear the desired principal high frequency Xy' shear mode. In the case ofthe BT cut crystals, for example, the above-mentioned interfering modesnear the high frequency Xv shear mode are given by:

fzr= 2 n, kilocycles per second f t= n kilocycles per second fz'a nkilocyclcs per second f=r= g n, kilocycles per second f g n kilocyclesper second fl'I g 11,, kilocycles per second While it is possible tochoose different or unequal values for the X and Z dimensions of thecrystal plate, it has been found that over an extended range offrequencies as from 3 to 10 megacycles per second the same or equalvalues therefor are possible, resulting in square crystal plates. Thisis a decided advantage in manufacture. It is to'be noted that theabove-mentioned equations give rules for dimensioning that include onlythe three principal interfering modes of simple orders. A more completedescription of the above relation is given in a paper by R. A. Sykesentitled Modes of motion in quartz crystals, The eflects of coupling andmethods of dedesign, Bell System Technical Journal, January 1944.

The thickness mode AT or BT cut quartz crystal plate I may also bethickness shaped by making it very slightly thicker in the center regionthan at the peripheral edges thereof in order to improve the activity ofthe desired thickness shear mode of vibration. By vacuum baking the barecrystal element I just before laying down the metal coatings 2 and 3,gas molecules on the surface of the crystal plate I may be removed witha resulting improved quality for the electrode coatings 2 and 3,

Accordingly, a number of variables associated with the crystal plate Imay determine or govern its activity performance. These factors includethe major face area of the crystal plate I, the area and quality of theplated electrodes 2 and 3, the thickness shaping of the crystal plate I,and spurious modes of motion that may be present therein, as mentionedhereinbefore; and also the damping that may be introduced therein by themounting, and the relation of the crystal characteristics such as thecrystal static capacitance to the circuit capacitance in which it may beconnected.

The relation of the piezoelectric activity PI of the crystal element Iwith respect to the static capacitance Co thereof and the circuitcapacitance C which may be connected across or in shunt with the crystalelement I is given by:

As indicated by the last-mentioned equation, the piezoelectric activityis a maximum when the static capacitance Co of the crystal element Iequals the circuit capacity C that may be connected across the crystalelement I; and since Co is proportional to the effective area of theelectrodes 2 and 3, this establishes the optimum area for the electrodes2 and 3 for a particular value of the shunt circuit capacity C which maybe used with the electroded crystal element I.

While the crystal element I has been particularly described as athickness shear mode quartz crystal element of the AT or BT cut type, itwill be understood that it may be a thickness shear mode quartz elementof another orientation or out than the AT or BT cut mentioned, or thatit may be a thickness mode quartz element of the longitudinal mode type,or a quartz or other element of any type that may be supported at one,two or more of its corners or edges by means of a spring wire coil lahaving its adjacent turns thereof sprung over a corner or over an edgeof the crystal element I. Also, while a quartz element I has beenparticularly described, it will be understood that the crystal element Imay be any suitable piezoelectric element such as, for example, acrystal element cut from Rochelle salt, or from ammonium dihydrogenphosphate, potassium dihydrogen phosphate, or the correspondingarsenates.

As illustrated in Fig. 1, the electrode coatings 2 and 3 may be reducedarea electrodes partially covering the opposite major faces of thecrystal element I and leaving uncovered the marginal portions thereof,except for the narrow connection coatings which may extend to thediagonally opposite corners of the crystal element I for makingindividual electrical connections with the spring wire supports 4a and5a. As illustrated in Fig. 1, the overlapping oppositely disposedportions of the electrode coatings 2 and 3 may be substantially circularor they may be alternatively square or rectangular in shape forapplyingan electric field of selected shape and area to the centralportion only of the crystal element I. Effective field producingelectrodes of substantially circular shape are disclosed, for example,in S, C. Hight Patent 2,343,059 granted February 29, 1944, onapplication Serial No. 357,251 filed September 18, 1940.

Such partial or reduced area field producing electrodes 2 and 3 may bemade of a selected area relative to the major face area of the crystalelement I in order to obtain a selected value of impedance for theelectroded crystal element I. In cases where it is desired to fix theimpedance between the electrodes 2 and 3 at a certain value such as, forexample, to match the capacitance of the electroded crystal element Iwith the capacitance of the circuit that may be connected therewith, theoppositely disposed or overlapping portions of the electrodes 2 and 3may be made of an area calculated to provide such value of capacitanceor impedance.

The reduced area centrally located I lectric field produced by thepartial electrodes 2 and 3 may be made of a selected value relative tothe major face area of the crystal element I in order to increase theactivity of the crystal element I and reduce the number of spuriousfrequencies therein. This effect results from removing the excitingfield from the outer marginal or peripheral portion of the crystalelement I and confining the excitation to a more limited central areaonly, thereby reducing the number and magnitude of undesired spuriousfrequencies generated in the crystal element I. The reduced areaelectrode coatings 2 and 3 also are useful to reduce wear at themarginal or comer points of supports 4a and 5a of the crystal element I.In this arrangement the edges and corners of the crystal element I beingisolated from the active central vibratory portion within the influenceof the field produced by the oppositely disposed central portions of theelectrodes 2 and 3 are relatively motionless and accordingly may bethere mounted and electrically connected without wearing away theconductive coatings 2 and 3 at the corner points of mounting adjacentthe coiled spring wires to and 5a.

While in Fig. 1 the electrode coatings 2 and 3 are illustrated asextending to two of the diagonally opposite corners of the crystalelement I, they may extend to two adjacent corners thereof, or to anyparts of the edges thereof, to suit the location of the coiled springsto and 5a with which they may be electrically connected.

The integral conductive coatings 2 and 3 may consist of one or morefilms or layers of metallic or conductive material such as gold,platinum, silver, nickel, aluminum, chromium or other conductivematerial applied to the quartz or other crystal element I by anysuitable method or process such as spraying, evaporation in vacuum,electroplating or otherwise. 'The metallic coatings 2 and 3 may beapplied using a mask or shield over the portions of the crystal elementI where no metallic deposit is desired. If no mask has been employedduring the metallic coating process, the undesired portions of thecoatings near the edges of the crystal element I may be etched offafterwards, or otherwise removed or segregated electrically andmechanically, to form the eflective reduced area electrode coatings 2and 3. The frequency of the metal coated crystal element I may beadjusted by control of the thickness of the metallic platings 2 and 3 onits surfaces, the frequency being lowered by adding metal or raised byremoving metal from one or both major surfaces of the crystal element I.Where the metallic coatings 2 and 3 are applied by evaporation in vacuumor by spraying, for example, the crystal element I may be connected in asuitable circuit and oscillated at its natural frequency while applyingthe metal coating, the coating process being cut oil or stopped when thefrequency of the metallized crystal plate I reaches the desired value.

In any process described herein, the unplated crystal blank I may beground to a frequency above that desired by an amount given by:

f=kfo where 10 is the final desired frequency and Af of the crystal.oration chamber is reduced to a 'sumciently is the increase in frequencyfor which the unplated crystal blank I must be ground. This insures thata uniform thickness of film for the electrodes 2 and 3 will result onall crystals when adjusted to the final frequency. For example, whenusing crystal blanks I from to 10.6 millimeters square and electrodes 2and 8 of 6 millimeters diameter the above given equation reduces to:

Af=1.39fo 10- cycles per second At a frequency of 5000 kilocycles persecond this results in a crystal blank I ground 35 kilocycles per secondhigher in frequency. The first or basic coatings for the electrodes 2and 3, illustrated by the basic coating 3b in Fig. 3, are deposited forexample by gold bright spray or evaporated gold in a vacuum to athickness of between threequarters to the full amount required to bringthe ard crystal and test crystal controlling these two oscillators. Theoutput of the two oscillators referred to may be connected to amodulator, the output of which gives the frequency difference referredto. With a suitable circuit, the frequency difierence may be read on acalibrated milliammeter.

The additional amount of film to be deposited to constitute theelectrodes 2 and 3, as illustrated for example at 30 in Fig. 3, may bedetermined by the use of the duplicator referred to by observing thefrequency difierence from that of a standard crystal of the desiredfinal frequency. When the final frequency adjustment is made byelectroplating the additional metal the current and time may be socontrolled as to electroplate at a fixed rate and as for example 500cycles per second. By observation of the frequency difference, the timeof plating may be accurately determined. By using a series of successiveplatings, the accuracy of the final frequency adjustment may be made asprecise as desired. When the final frequency adjustment is made byevaporation of a metal, the crystal may be connected to an oscillatorwhile it is in the vacuum chamber. Using a mask placed close to, but nottouching, the crystal the evaporated metal film may be restricted to thecentral part When the pressure in the evaplow value the electricallyheated filament used orated metal on the central portion of the crystalmetallize and adjust the final frequency of the coated crystal elementI, the initial coating applied to the bare crystal element I may be, for

example, gold bright applied by spraying or gold applied by evaporationin vacuum, or other metal that will readily take an additional coatingof electroplate thereon, such as gold. nickel or otherwise. The coatings3a and 3b of Fig. 3 may serve to illustrate the outer and inner coatingsrespectively of the electrode coating 8 for example. As an example, thebasic gold electrode forming part of the electrode films 2 and 3 may beformed on the bare crystal element I by spraying and baking thereonliquid gold bright of any suitable composition. Liquid bright gold is amaterial which has long been used for the decoration of china andglassware and is primarily a solution of gold resinate in a suitableorganic solvent. Noble metals other'than gold, such as platinum,rhodium, palladium, are often incorporated into the solution and can bedeposited from the resinous film resulting after drying out the solventby heating to temperatures above 400 C.

When fired at such elevated temperatures, the adhesion of films is verygood and in the case of crystalline quartz the baking temperature may besafely up to 540 C. The liquid bright gold solution may be applied onthe bare crystal element I by means of a controlled air-brush spray, andthe liquid gold bright solution may be supplied to the air-brush from aclosedbottle. The amount of gold in the electrode coatings 2 and 3 is ofsome importance since it may be used as the first step in the adjustmentof the crystal frequency, as well as acting as the electrodes for thecrystal element I. The gold may be applied in two or more separatespraying operations to more completely fire out carbonaceous matter fromthe gold layer and to cover up any pinhole areas in the coating of goldresulting from the first spraying operation. The crystal element I withits basic gold or other integral metallic films forming part of theelectrode coatings 2 and 3 may then be mounted at its diagonallyopposite corners between adjacent turns of the small coil springs 4a and5a and the ends of the spring and gradually lowering the frequency ofthe coated crystal element I, as may be observed on the calibrated meterof the duplicator. When the frequency difference becomes zero or anyassigned value, the current in the evaporator filament may be turned 06,the coated crystal element I being thereby adjusted to final frequency.Using two small evaporators and a high speed vacuum pump with a singleduplicator, an operator may adjust to final frequency as many as 100crystals per hour.

Where the electroplating method is used to 76 wires to and 5a maybesecured to the coatings 2 and 3 respectively, by means of a spot 20 ofsolder, or conductive plastic cement, or by electroplating.

As illustrated in Fig. 1 and also in Figs. 2 and 3, each of the springwire supporting coils 4a and 5a may be in the form of. a helix, adjacentturns of which may be sprung over an edge of the crystal element I atone of the four corners thereof. One turn of the coil 4a may be incontact with the bare crystal element I and the other or adjacent turnof the coil 4a forming the end portion of the wire 4 may be in contactwith the crystal electrode coating 2, the axis of the coil 4a beinggenerally in a direction perpendicular to the major faces of the crystalelement I. The construction and mounting arrangement for the supportingcoil 5a may be the same as that of the coil 4a except for being placedat the diagonally opposite corner of the crystal element I with the endof the wire 5a in contact with the crystal electrode coating 3, asillustrated in Fig. 1. The turns of the coils 4a and 5a are arranged incontact with one but not both of the electrode coatings 2 and 3 to avoidshort circuiting thereof and to provide individual electrical;connections therefor. The wire coils 4a and 5a function as a mechanicalsupporting agent and as an electrical connection agent the springclamping action exerted on the comers of the crystal element I, they mayserve to reduce undesired spurious resonances in the crystal element I.

The ends of the spring wires 4a and in may be secured directly to thecrystal electrode coatings 2 and 3 respectively, by means of a spot ormass 20 of conductive plastic cement placed within the coil turn andover the ends of each of the wires 4a and 5a as illustrated in Figs. 2and 3. The spot of cement 20 may be applied in paste form at thejunction of the wires 4a and 5a with the crystal electrode coatings 2and 3 respectively, by means of a pointed applicator or similarinstrument to avoid getting the cement 20 outside the wire loops 4a and5a. The amount of cement 20 used need be only enough to obtain coverageof the crystal corners and wire surfaces as illustrated at 20 in Figs. 2and 3. The cement 20 in paste form may be dried and baked in an oven orby an infra-red lamp, for example, at a temperature suflicient to causeit to thermoset thereby providing a good mechanical bond with goodelectrical conductivity for securing the wires 4a and 5a to the crystalcoatings 2 and 3 respectively. As an example, the conductive plasticcement 20 may consist of finely divided silver powder or other suitableconductive powder admixed with a suitable plastic binder such asBakelite cement; The amount of powdered silver admixed with the Bakeliteadhesive may be substantial or suflicient to render the spot of adhesive20 electrically conductive. The mass 20 of conductive plastic cementfunctions as a mechanical supporting agent and as an electricalconnective agent for the crystal element I and also, by reason of itsplasticity, may serve to damp out undesired spurious frequencies thatmay be present in the corners of the crystal element I.

As mentioned hereinbefore, the assembled wiremounted electroded crystalelement I may be electroplated to final frequency in one or moreelectroplating steps by the electrodeposition of an additional coatingof nickel or other suitable metal of proper mass on top of the goldbright or other basic coatings previously formed on the bare crystalelement I. By suitable control of the electroplating current and thetime required for deposit of a predetermined amount of metal forming theelectrode coatings 2 and 3, the frequency of the electroplated crystalelement I may be adjusted to a desired value. Any suitable timing andplating circuit may be used for the timing and current control of theelectroplating. The plating current may be adjusted to produce a timedfrequency change per second of plating time. In the case of nickelplating, electrolytic nickel or other high purity nickel anodes may beused. As an example, the solution for nickel plating may consist of abath including nickel sulphate with suflicient nickel chloride presentto insure good anode corrosion, and sumcient boric acid present to buffthe cathode film and prevent it from becoming alkaline and suflicientnickel hydroxide present to insure high cathode efficiency. The solutionmay be treated with activated charcoal to remove impurities. In the caseof nickel plating on a gold bright film base, there is an initialreduction of the gold bright base which may be compensated for byallowing extra plating time.

Alternatively, the additional coating of metal may be put on to form thecrystal electrodes 2 and 3 by evaporating additional metal thereon invacuum. The evaporated metal may be applied thereto while the crystalelement I is being oscillated at its resonance frequency connected incircuit with a suitable oscillator circuit. The layer of additionalmetal thus put on to form the electrode coatings 2 and 3 adds to theloading of the crystal element I andgradually lowers its frequency. Thedeposition of the evaporated metal may be stopped when th observeddesired frequency has been reached.

The frequency of the electroded crystal element I. may also be adjustedto final value by applying thereto a coating of non-conductive loadingmaterial such as silicon chloride. The coating of silicon chloride'notonly loads the crystal element I and thereby lowers its frequency butalso forms an enclosing protective coating therefor. As an example, thesilicon compound may be applied as a solution of silica sol. The silicasol solution is a suspension of hydrated silica in acetone containing aplasticizer of polyvinyl acetate, and may be prepared by adding to ethylalcohol normal hydrochloric acid solution and adding slowly to thissolution tetraethyl silicate while the alcohol acid solution is beingagitated. The solution will become noticeably warm as a result of thehydrolysis of the silicate and a clear suspension of extremely finelydivided hydrated silica is thus obtained. When the suspension is cooled,acetone in which the polyvinyl acetate has been dissolved may be addedand the solution is ready for use. The solution when sprayed onto thesurfaces of the crystal element I sets quickly to a rigid solid and byspraying the crystal element I while it is oscillating at its naturalfrequency, it is possible to decrease the frequency continuously whileat the same time observing the decreasing frequency. Any typ of spraygun or chamber that applies a fine moist spray to one or to both majorfaces simultaneously of the crystal element I may be used.

As illustrated in Fig. 1, the supporting spring wires 4 and 5 may bestraight upright wires of equal length carried :by terminal pins 6 and Ifor supporting and establishing individual electrical connections withthe crystal element I. The spring wires 4 and 5 may consist of steel,phosphor bronze or other conductive spring wire material of relativelysmall but sufiicient diameter'to support the crystal element I from theterminal pins 6 and I. The lower ends of the supporting spring wires 4and 5 may be individually sprung around the terminal pins 6 and 'I andsecured thereto, as by solder. The upper ends of the spring wires 4 and5 terminating in the spring wire coils 4a and 5a respectively may beconstructed either from the same wire material or from different wirematerials that may be soldered or otherwise connected togetherelectrically and mechanically. The upright wires 4 and 5 may havecircular or other shaped resilient bends therein for resilientlysupporting the crystal element I, as illustrated, for example, in A. W.Ziegler Patent 2,275,122, dated March 3, 1942. The spring wire uprights4 and 5 may be so adjusted as to have the crystal element I free frompressure or tension thereon from the springs 4 and 5.

The pin-type terminal prongs 8 and I may be provided with corrugations 8therein which may be firmly embedded in a base I0 forming one wall of anenclosing container which may consist of the base I 0 and a sealedenclosing cover II for the crystal element I. The container base I0 andits cover II may be composed of molded material such as Bakelite, glass,ceramic or other suitable material. The cover I I may be secured to thebase III by a pairof screws I2 disposed'at opposite ends or sides of thebase II). A gasket I3 may extend around the entire bottom edge of theenclosing cover II between the cover II and the base III in order toprovide an hermetic seal for th enclosing container I and II.Alternatively, the cover II may be secured to the base I0 by fusion. Inthe case of a base Ill and a cover II composed of glass or ceramicmaterial, the base Ill and cover II may .be joined'together around theentire outer edge periphery by applying narrow strips I4 and I5 of bakedsilver paste, for example, to the adjacent edges or the base I 0 andcover II and soldering the baked silver paste strips I4 and I5 togetherby means of a narrow rib I8 of solder.

The sealed crystal container I 0 and I I may contain dry air or otherinert gas, which may be heavier or lighter than air, and of suitabledensity and pressure which may be greater or less than atmosphericpressure, to control the damping or the frequency of either the desiredor undesired resonance in the crystal element I.

The enclosing container Ill and II when composed of glass or otherdielectric material may be made toserve as the dielectric of anadjustable electrical condenser by providing oppositely disposed metalcoatings I8 and I9 of baked silver paste, for example, on a portion orportions of the inner and outer walls thereof. The inside wall of thedielectric container in may be partially or entirely metallized by theintegral conductivecoating I8, and the outside thereof may be partiallymetallized by the conductive coating I8. By adding or subtracting fromthe area of the outside coating I8, the final adjustment of thecapacitance of the condenser comprising the electrodes i8 and I9 and thedielectric II therebetween may be made. The condenser electrodes I8 andI9 may be associated with the crystal element I in an suitable mannersuch as by connecting in series or parallel circuit relation therewithin a known manner for the purpose of providing a close adjustment of theresonant or antiresonant frequency.

Where the container base Ill and cover II are composed of Bakelite, forexample, or a gasket I3 of "neoprene artificial rubber, for example, isused, such materials may gradually give of! volatile materials which maybe absorbed by the metal of the crystal electrodes 2 and 3 with aresulting slight decrease in frequency of the electroded crystal elementI over a period of time. To filter out, absorb and prevent such volatilematerial or moisture from reaching the crystal element l and itselectrodes 2 and 3, paper shields or liners, for example, which may beimpregnated with charcoal or other suitable absorbing agent, forexample, may be inserted as at I9 in Fig. 1 along the entire inner wallof the container Ill and II.

As illustrated in Fig. 1, a massed weight 24 or 25 may be secured to andsuspended by either or both of the supporting spring wires 4 and 5 at anode of motion therein in order to reflect motion transmitted to thewire 4 or 5 from the vibratory crystal element I to thereby prevent suchwire motion from adversely afiecting the desired crystal frequency asdisclosed in United States Patent 2,371,613, granted March 20, 1945, toI. E. Fair on an application, Serial No. 470,759, filed December 31,1942. The massed weight 24 or 25 may be in the form of a single ball,disc or globule of solder or a thin metal disc soldered to each or thewires 4 and 5 at a node of m t therein, as disclosed in theabove-mentioned patcut to I. E. Fair. Alternatively, to obtain freedomfrom the vibrational eifect or'the wire support system upon the motionof the crystal element I, a structure which is equivalent to amechanical filter may be made by loading either or both of the wires 4and i with additional massed weights 26 secured to the wires 4 and I atdefinite intervals theron. As illustrated in Fig, 1, the combination ofthe wire 5, for example, loaded with massed weights 25 and 28 atdefinite intervals thereon is equivalent to a filter structure where MIis the mass of the section of the wire 5 between the crystal element Iand up to the first weight 25 having a mass M2, and CI is the complianceof that section of the wire 5. This filter is equivalent to a low-passfilter of the infinite type with its low pass cut oil occurring whenM2/2 resonates the compliance CI. The impedance is one which goesthrough zero at the resonance MI, CI at which point the loading effectof the wire on the crystal element I will be small. A second weight 26similarly spaced, on the wire 5 additionally decreases the eifectof theend termination on the resonance of the crystal element I.

Although this invention has been described and illustrated in relationto specific arrangements, it is to be understood that it is capable ofapplication in other organizations and is, therefore, not to be limitedto the particular embodiments disclosed but only by the scope of theappended claims and the state of the prior art.

What is claimed is:

1. A conductive wire support for a piezoelectric crystal elementcomprising a spring wire coil of substantially helical form havingadjacent turns thereof sprung over and straddling a corner edge only ofsaid crystal element and exerting a 4 clamping pressure on said cornerin a direction substantially normal to the major faces of said crystalelement.

2. A conductive wire support for a piezoelectric crystal elementcomprising a spring wire coil of substantially helical form havingadjacent turns thereof sprung over and straddling a comer edge only ofsaid crystal element and exerting a.

clamping pressure on said corner in a direction substantially normal tothe major faces of said crystal element, and means including aconductive spring wire comprising an extension of the wire forming saidspring wire coil for supporting said spring wire coil and said crystalelement.

3. A conductive wire supporting system for a piezoelectric crystalelement having an electrode coating formed integral with a major facethereof comprising a conductive spring wire coil of substantiallyhelical form having two adjacent turns thereof sprung over andstraddling an edge of said crystal element, one of said adjacent turnsof said coil being in contact with said electrode coating on said majorface adjacent said edge of said crystal element, and the axis of saidspring wire coil being substantially perpendicular to said major face ofsaid crystal element.

4. A conductive wire supporting system for a piezoelectric crystalelement having an electrode coating formed integral with a major facethereof comprising a conductive spring wire coil of substantiallyhelical form having two adjacent turns thereof sprung over andstraddling an edge of said crystal'element, one of said adjacent turnsof said coil being in contact with said electrode coating on said majorface adjacent said edge of said crystal element, the axis of said springwire coll being substantially perpendicular to said major face of saidcrystal element, conductive adhesive means for securing the wire of saidone of said turns to said electrode coating, and means including aconductive spring wire comprising an extension of the wire forming saidspring wire coil for supporting said spring wire coil and said crystalelement.

5. Piezoelectric crystal apparatus comprising a piezoelectric crystalelement, electrodes on the opposite major faces of said crystal elementcomprising conductive coatings formed integral with said major faces andextending independently to different corners of said crystal element,and conductive supports contacting said coatings adjacent said comersonly and establishing individual electrical connections with saidelectrode coatings, each of said supports comprising a spring wireterminated in a spring wire coil having adjacent turns thereof sprungover and holding one only of said corners in contact with one of saidelectrode coatings, the axis of each of said spring wire coils beingsubstantially perpendicular to said major faces of said crystal element.

6. Piezoelectric crystal apparatus comprising a piezoelectric crystalelement having substantially rectangular major faces, conductivecoatings formed integral with the opposite major faces and extendingindependently to diagonally opposite corners of said crystal element,means including conductive supporting spring wires terminated in springwire coils each having adjacent turns sprung over one only of saidcorners for mounting said crystal element at said corners and forestablishing individual electrical connections with said coatings atsaid corners, and conductive adhesive means securing said wire coils tosaid corners and establishing individual electrical connections withsaid conductive coatings at said corners.

7. A thickness-mode piezoelectric crystal element having substantiallyrectangular opposite major faces, the thickness of said crystal elementbetween said opposite major faces being made of a value corresponding tothe value of said thickness-mode frequency thereof, a pair of conductivecoatings formed integral with said opposite major faces, said conductivecoatings being disposed opposite each other at the central portions onlyof said major faces and forming electric field-producing electrodesspaced entirely inwardly of all of the peripheral edges of said majorfaces, one of said coatings on one of said major faces extending to onecorner of said crystal element and the other of said coatings on theother of said major faces extending to another comer of said crystalelement, conductive supporting spring wires comprising a pair of springwire coils each having adjacent turns sprung over one of said cornersfor mounting said crystal element at said corners and establishingindividual electrical connections with said coatings at said corners,and conductive adhesive means securing said supporting wires to saidcorners and establishing individual electrical connections with saidconductive coatings at said corners.

8. A thickness-mode piezoelectric quartz crystal element havingsubstantially rectangular 0p posite major faces, the thickness of saidcrystal element between said opposite major faces being made of a valuecorresponding to the value of said thickness-mode frequency thereof, apair of conductive coatings formed integral with said opposite majorfaces, said conductive coatings being disposed opposite each other atthe ccntral portions only of said major faces and forming electricfield-producing electrodes spaced entirely inwardly of all of theperipheral edges of said major faces, one of said coatings on one ofsaid major faces extending to one corner of said crystal element and theother of said coatings on the other of said major faces extending toanother corner of said crystal element, conductive supporting springwires comprising a pair of spring wire coils each having adjacent turnssprung over one of said comers for mounting said crystal element at saidcorners and establishing individual electrical connections with saidcoatings at said corners, and conductive adhesive means comprisingconductive plastic cement securing said supporting'wires to said cornersand establishing individual electrical con nections with said conductivecoatings at said corners.

9. A thickness-mode piezoelectric quartz crystal element havingsubstantially rectangular opposite major faces, the thickness of saidcrystal element between said opposite major faces being made of a valuecorresponding to the value of said thickness-mode frequency thereof, apair of conductive coatings formed integral with said opposite majorfaces, said conductive coatings being disposed opposite each other atthe central portions only of said major faces and forming electricfield-producing electrodes spaced entirely inwardly of all of theperipheral edges of said major faces, one of said coatings on one ofsaid major faces extending to one comer of said crystal element and theother of said coatings on the other of said major faces extending to thediagonally opposite corner of said crystal element, conductivesupporting spring wires comprising a pair of spring wire coils eachhaving adjacent turns sprung over one of said corners for mounting saidcrystal element at said corners and establishing individual electricalconnections with said coatings at said corners, and conductive adhesivemeans securing said supporting wires to said corners and establishingindividual electrical connections with said conductive coatings at saidcorners.

10. A thickness-mode piezoelectric quartz crys" tal element havingsubstantially rectangular opposite major faces, the thickness of saidcrystal element between said opposite major faces being made of a valuecorresponding to the value of said thickness-mode frequency thereof, apair of conductive coatings formed integral with said opposite majorfaces, said conductive coatings being disposed opposite each other atthe central portions only of said major faces and forming substantiallycircular shaped electric field-producing electrodes spaced entirelyinwardly of all of the peripheral edges of said major faces, one of saidcoatings on one of said major faces extending to one corner of saidcrystal element and the other of. said coatings on the other of saidmajor faces extending to the diagonally opposite comer of said crystalelement, conductive supporting spring wires comprising a pair of springwire coils each having adjacent turns sprung over one of said diagonallyopposite corners for mounting said crystal element at said corners andestablishing individual electrical connections with said coatings atsaid corners, and conductive adhesive means securing said supportingwires to said corners and establishing individual electrical connectionswith said conductive coatings at said corners, the thickness of saidcrystal coatings being made of a value corresponding to the value of thethickness-mode frequency desired for said coated crystal element, andsaid coatings comprisin gold applied to said crystal element.

11. A thickness-mode piezoelectric quartz crystal element havingsubstantially rectangular opposite major faces, the thickness of saidcrystal element between said opposite major faces being made of a valuecorresponding to the value of said thickness-mode frequency thereof, apair of conductive coatings formed integral with said opposite majorfaces, said conductive coatings being disposed opposite each other atthe central portions only of said major faces and formingelectricfield-producing electrodes spaced entirely inwardly of all of theperipheral edges of said major faces, one of said coatings on one ofsaid major faces extending to one comer of said crystal element and theother of said coatings on the other of said major faces extending to thediagonally opposite corner of said crystal element, conductivesupporting spring wires comprising a pair of spring wire coils eachhaving adjacent turns sprung over one of said diagonally oppositecorners for mounting said crystal element at said corners andestablishing individual electrical connections with said coating ,atsaid comers, and conductive adhesive means securing said supportingwires to said corners and establishing indi-- vidual electricalconnections with said crystal coatings at said corners, the thickness ofsaid crystal coatings being made of a value corresponding to the valueof the thickness-mode frequency desired for said coated crystal element,and said coatings comprising an electroplated metal.

12. A thickness-mode piezoelectric crystal element having substantiallyrectangular shaped opposite major faces, the thickness of said crystalelement between said opposite major faces being made of a valuecorresponding to the value of the thickness-mode frequency of saidcrystal element, a pair of substantially equal size and oppositelydisposed field-producing conductive coatings formed integral with thecentral portions of said opposite major faces and spaced entirelyinwardly of all of the peripheral edges of said major faces, and a pairof relatively narrow connective conductive coatings formed integral withsaid opposite major faces and extending from said field-producingconductive coatings to two different corners of said crystal element,conductive supporting spring wires comprising a pair of spring wirecoils each having adjacent turns sprung over one of said corners formounting said crystal'element at said corners and establishingindividual electrical connections with said coatings at said corners,and conductive adhesive means securing said supporting wires to saidcorners ,and establishing individual electrical connections with saidconductive coatings at said corners. v

13. A thickness-mode piezoelectric quartz crystal element havingsubstantially rectangular shaped opposite major faces, the thickness of,said crystalelement between said opposite major portions of saidopposite major faces and spaced entirely inwardly ofall of theperipheral edges of said major faces, and a pair of relatively narrowconnective conductive coatings formed integral with said opposite majorfaces and extending independenly from said field-producing conductivecoatings to two diagonally opposite corners of said crystal element,conductive supporting spring wires comprising a pair of spring wirecoils each having adjacent turns sprung over one of said diagonallyopposite corners for mounting said crystal element at said cornersand'establishing individual electrical connections with said coatings atsaid corners, and conductive adhesive means securing said supportingwires to said diagonally opposite corners and establishing individualelectrical connections with said conductive coatings at said -corners.

14. A thickness-mode piezoelectric quartz crystal element havingsubstantially rectangular shaped opposite major faces, the thickness ofsaid crystal element between said opposite major faces being made of avalue corresponding to the value of the thickness-mode frequency of saidcrystal element, a pair of oppositely disposed field-producingconductive coatings formed integral with the central portions of saidopposite major faces and spaced entirely inwardly of all of theperipheral edges of said major faces, and a pair of relatively narrowconnective conductive coatings formed integral with said opposite majorfaces and extending independently from said field-producing conductivecoatings to two diagonally opposite comers of said crystal element,conductive supporting spring wires comprising a pair of spring wirecoils each having adjacent turns sprung over one of said corners formounting said crystal element at said diagonally opposite corners andestablishing individual electrical connections with said coatings atsaid corners, and conductive adhesive means comprising conductiveplastic cement securing said supporting wires to said corners andestablishing individual electrical connections with said conductivecoatings at said corners. Y

15. Piezoelectric crystal apparatus comprising a piezoelectric crystalelement having conductive electrode coatings formed integral with theopposite major faces thereof, and supporting conductive spring wirecoils each having adjacent turns thereof sprung over and straddling anedge of said crystal element in contact with one of said electrodecoatings on one of said major faces, said coatings comprising basiccoatings on said major faces, and an additional or outer coatings addedupon at least a portion of one of said basic coatings, the mass Of saidadded coating being made of a value corresponding to the value of thefinal frequency desired for said coated crystal element for fixing saidfinal frequency thereof.

16. Piezoelectric crystal apparatus in accordance with claim 15 whereinsaid basic coatings comprise gold adhering to said crystal element, andsaid added coating comprises evaporated metal adhering to said basicgold coating.

17. Piezoelectric crystal apparatus in accordance with claim 15 whereinsaid basic coatings comprise gold adhering to said crystal element, andsaid added coating comprises electroplated nickel adhering to said basicgold coating.

ROGER A. SYmilS

